"The given key was not present in the dictionary." error decoding base64 encoded CMS structure

[audunn]

Hi,
I am trying to use your tool to decode some base64 CMS structure (from an S/MIME message). I am using the Data Converter tool of the asn.1 Editor but it does not decode showing an error of "The given key was not present in the dictionary."
This online decoder https://lapo.it/asn1js and and openssl do not seem to have an issue with it.
Also I am able to decode CMS structures from other messages, any idea as to what may be causing the error?
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[Crypt32]

I will take a look.

[Crypt32]

Got this. The problem is that your file uses indefinite length. I'm not supporting indefinite length, because it is not allowed in DER encoding. It is supported by BER, but X.509 uses DER encoding.

[audunn]

Thank you, missed that.
Is there a quick way to see this from the file?

[Crypt32]

What exactly?

[audunn]

Sorry for not being clear. I am not familiar with those structures, what I mean is there a way to easily tell if a structure such as this is using indefinite length or definite or what encoding it is?

[Crypt32]

You can convert this Base64-encoded string to a byte array and examine 2nd byte. If it is 0x80 (128), then ASN type uses indefinite length. DER forbids indefinite length encoding on the grounds that serialized representation of the same data may change on re-encoding. Since my ASN.1 Editor is primarily intended to decode X.509 objects and they explicitly use DER encoding, indefinite length decoding is not implemented in my code.

[FranklinYu]

@Crypt32 I understand that BER is out-of-scope for this decoder, but the error message can be improved.

@audunn You can still see (not edit) the inner structure with some online tool like https://lapo.it/asn1js/

[ralienpp]

@FranklinYu, you mean that the tool could instead say "This is a BER-encoded file, but only DER is supported"?